Chlorotrimethylsilane

The title compound, C₃H₉ClSi, is liquid at room temperature. It was crystallized in situ on the diffractometer in a cold N₂ gas stream, forming a single crystal. The (CH₃)₃SiCl molecule lies on a crystallographic mirror plane. The bond distances are Si-Cl 2.0863 (9) Å and Si-C 1.843 (3) and 1.845 (3) Å.

S1. Comment

Alkylchlorosilanes such as (CH₃)₃SiCl, (CH₃)₂SiCl₂ and CH₃SiCl₃ are useful monomers in macromolecular organosilicon chemistry. Hydrolyzation of these chloromethylsilanes yields linear siloxanes and in this reaction the title compound, (I), (CH₃)₃SiCl, functions as a terminal chain group. However, crystal structure determinations of these important industrial chemical compounds have not previously been carried out. Here, the crystal structure of the first member of the chloromethylsilanes, chlorotrimethylsilane, (I), is reported.

The title compound is liquid at room temperature and melts at 176 K, so a single-crystal was grown at that temperature using the technique described below. Compound (I) crystallizes in the monoclinic space group P2₁/m, the molecule occupying a special position on the crystallographic mirror plane. The Cl, Si and one C atom, plus one H atom, lie in that plane. There is no indication of rotational disorder of the methyl groups.

The C—Si bond lengths of 1.843 (3) and 1.845 (3) Å are comparable with the corresponding bond lengths obtained by the structure determinations of 2,5-dichloro-2,5-dimethyl-2,5-disilahexane [1.848 (2) and 1.862 (2) Å; Ovchinnikov et al., 1985], chlorotricyclohexylsilane [1.871 (3) and 1.875 (2) Å; Lindfors et al., 1998] and chlorotriphenylsilane [1.852 (3) and 1.871 (2) Å; Lobkovskii et al., 1981]. The Cl—Si bond length of 2.0863 (9) Å in (I) can also be compared with that of the cited investigations of chlorinated silanes [2.074 (1) (Lobkovskii et al., 1981); 2.091 (1) (Ovchinnikov et al., 1985) and 2.087 (1) Å (Lindfors et al., 1998)].

The C—Si—C bond angles [111.9 (1) and 112.6 (2)°] are larger than tetrahedral, while the C—Si—Cl angles [106.6 (1) and 106.9 (1)°] are significantly smaller than tetrahedral. In contrast with the polymeric crystal structure of (CH₃)₃SnCl (Hossain et al., 1979; Lefferts et al., 1982), which exhibits short intermolecular Sn···Cl contacts of 3.269 (2) Å with a coordination number of 4 + 1 for the Sn atom, compound (I) is obviously tetracoordinated, with intermolecular Si···Cl contacts of 4.206 (2) Å. This is larger than the sum of the van der Waals radii (3.9 Å) for Si and Cl. Thus, the linear Cl—Si—Cl chain of the chlorotrimethylsilane structure [intermolecular Cl—Si—Cl angle of 179.9 (2)°] is comparable with the linear Cl—Sn—Cl chain in the (CH₃)₃SnCl crystal.

S2. Experimental

The title compound was condensed into a small thin-walled glass tube of 0.3 mm diameter, filling 4 mm at its tip. It was then sealed off to a length of 30 mm and fixed to an arcless and heat-insulated goniometer head, using which the sample was placed in the centre of a four-circle X-ray diffractometer equipped with an integrated N₂ gas stream cooling device of in-house construction (Dietrich & Dierks, 1970). The crystal was grown in situ in the cold N₂ gas stream by a process similar to pulling a single-crystal from the molten substance, applying an electronically controlled coil of heating wire around the sample glass tube. It was cooled down further for the measurement.

S3. Refinement

With regard to the completeness of the reflection measurement, 86.4% of all possible unique reflections with Bragg angles below θ_max were measured; 153 reflections are missing from the region 52° < 2θ < 62°, while 271 reflections from this region were measured. The reason for this is that the measurement had to be stopped early, because of the progressive crystal damage which was occurring. It is difficult and time-consuming to produce a single-crystal in situ on the diffractometer, and such crystal destruction would be present again in any repeat of the experiment. Therefore, a new data collection of these missing reflections was not attempted. A possible explanation for the large radiation-induced decay of the crystal is that the Mo Kα radiation destroys the quasi-polymeric intermolecular Cl—Si···Cl orientation. The data were successfully corrected for this phenomenon by the usual scaling to the standard reflections.

Computing details

Data collection: Stoe software; cell refinement: Stoe software; data reduction: Stoe routine REDUC; program(s) used to solve structure: SHELXS90 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1971); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The molecular structure of (I) showing 50% probability displacement ellipsoids and the atom-numbering scheme. H atoms are drawn as spheres of arbitrary radii [symmetry code: (i) x, 1/2 − y, z].

chlorotrimethylsilane

Crystal data

C3H9ClSi	Dx = 1.099 Mg m^−3
Mr = 108.64	Melting point: 176 K
Monoclinic, P21/m	Mo Kα radiation, λ = 0.7107 Å
a = 6.292 (1) Å	Cell parameters from 126 reflections
b = 7.735 (1) Å	θ = 8.0–17.3°
c = 6.745 (3) Å	µ = 0.63 mm^−1
β = 90.80 (1)°	T = 157 K
V = 328.24 (16) Å^3	Cylinder, colourless
Z = 2	0.8 × 0.3 × 0.3 mm
F(000) = 116

Data collection

Siemens four-circle single-crystal X-ray diffractometer with an open χ-circle of 100° and an integrated N2 gas stream cooling device.	971 independent reflections
Radiation source: fine-focus sealed tube	689 reflections with I > 2σ(I)
Nb filter monochromator	Rint = 0.021
Detector resolution: Conventional scintillation counter for measuring the X-ray reflections individually. pixels mm^-1	θmax = 31.0°, θmin = 3.0°
ω–2θ scan; Δω = 1.38° + 0.52° × tanω	h = −3→8
Absorption correction: analytical (the cylinder was approximated by an octagonal prism)	k = −10→9
Tmin = 0.853, Tmax = 0.864	l = −9→9
1216 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	Hydrogen site location: secondary
wR(F^2) = 0.096	All H-atom parameters refined
S = 1.12	w = 1/[σ^2(Fo^2) + (0.0422P)^2 + 0.0947P] where P = (Fo^2 + 2Fc^2)/3
971 reflections	(Δ/σ)max < 0.001
47 parameters	Δρmax = 0.45 e Å^−3
0 restraints	Δρmin = −0.22 e Å^−3

Special details

Experimental. (from above) Chlorotrimethylsilane was condensed into a small thin-walled glass tube of 0.3 mm diameter, filling 4 mm at its tip. It was then sealed off to a length of 30 mm and fixed to an arcless and heat-insulated goniometer head by which the sample was placed in the center of a four-circle X-ray diffractometer equipped with an integrated N2 gas stream cooling device of in-house construction (ref. 6). The crystal was grown in situ in the cold N2 gas stream by a process similar to pulling a single-crystal from the molten substance, applying an electronically controlled coil of heating wire around the sample glass tube. It was cooled down further for the measurement. With regard to the completeness of the reflection measurement it is so that 86.4% of all possible unique reflections with Bragg angles below theta_max were measured; and by numbers 153 reflections are missing from the region 52° < 2 theta < 62°, while 271 reflections from it were measured. The reason for this is that the measurement had to be stopped early, because of the progressing crystal damage occurring. It is hard and time consuming to produce a single-crystal in situ on the diffractometer, and the crystal destruction would be present again in a new experiment. Therefor, a new data collection of the not too many missing reflections was not tried. A possible explanation for the large, radiation induced decay of the crystal is that the Mo X-ray radiation destroys the quasi-polymeric intermolecular Cl—Si····Cl orientation. The data were successfully corrected for this phenomenon by the usual scaling to the standard reflections. The collimator used for the primary beam had 1.0 mm diameter openings at both ends.

Geometry. As Z is 2, only a half molecule constitutes the asymmetric unit, and the molecule is in special position on the mirror plane. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Si	0.68153 (11)	0.2500	0.31380 (10)	0.0333 (2)
C1	0.7633 (4)	0.0518 (4)	0.1838 (4)	0.0543 (6)
C2	0.7706 (6)	0.2500	0.5756 (5)	0.0474 (7)
Cl	0.34994 (10)	0.2500	0.31351 (12)	0.0467 (2)
H11	0.707 (5)	0.054 (5)	0.053 (5)	0.089 (10)*
H12	0.716 (5)	−0.048 (5)	0.235 (4)	0.071 (9)*
H13	0.912 (5)	0.050 (4)	0.186 (4)	0.069 (8)*
H21	0.927 (8)	0.2500	0.600 (7)	0.085 (14)*
H22	0.715 (4)	0.149 (4)	0.645 (4)	0.067 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Si	0.0258 (4)	0.0405 (4)	0.0336 (4)	0.000	0.0002 (2)	0.000
C1	0.0427 (12)	0.0639 (17)	0.0562 (14)	0.0087 (12)	0.0013 (10)	−0.0182 (13)
C2	0.0494 (18)	0.0523 (19)	0.0404 (15)	0.000	−0.0085 (12)	0.000
Cl	0.0268 (3)	0.0491 (5)	0.0642 (5)	0.000	0.0027 (3)	0.000

Geometric parameters (Å, º)

C1—H11	0.95 (4)	Si—C1	1.843 (3)
C1—H12	0.90 (4)	Si—C1^i	1.843 (3)
C1—H13	0.93 (3)	Si—C2	1.845 (3)
C2—H21	1.00 (5)	Si—Cl	2.0863 (9)
C2—H22	0.98 (3)
Si—C1—H11	109 (2)	C1—Si—C2	111.87 (11)
Si—C1—H12	115.9 (19)	C1^i—Si—C2	111.87 (11)
Si—C1—H13	107 (2)	C1—Si—Cl	106.57 (9)
Si—C2—H21	117 (3)	C1^i—Si—Cl	106.57 (9)
Si—C2—H22	110.7 (16)	C2—Si—Cl	106.92 (12)
C1—Si—C1^i	112.6 (2)

Symmetry code: (i) x, −y+1/2, z.